Under skies crowded by the warplanes of half a dozen countries, an assortment of factions backed by rival powers are battling one another in a dizzying array of combinations. Allies on one battlefront are foes on another. The United States, Russia, Turkey and Iran have troops on the ground, and they are increasingly colliding.

In the space of a single week last week, Russia, Turkey, Iran and Israel lost aircraft to hostile fire. The United States, meanwhile, has been battling for days to hold back Iranian-supported Syrian tribal militias in the eastern desert, drawing U.S. forces closer toward entanglement in Syria’s conflict.

“The risks are high,” said Sami Nadir of the Levant Institute for Strategic Affairs. “There is a new Cold War prevailing in Syria and any escalation could pave the way for a regional or international war given the fact that the big powers are directly present on the ground and not through proxies, as used to be the case in the past.”

The latest confrontations come after years of fighting during which the parties to what long ago ceased to be a civil war have come to rely on outside powers for their sustenance, bringing new weapons, soldiers and also agendas flooding into Syria.

With Assad having prevailed over the rebellion against him and the Islamic State squeezed into a last sliver of territory along the Iraqi-Syrian border, the rival players now are battling to shape the final outcome of the war.

The Syrian government controls the biggest chunk of territory, with over half the country at least under nominal control of Assad loyalists, backed by Russia and Iran.

The United States holds sway over the second-largest area, the 27 percent of Syria that was captured mostly from the Islamic State by Kurdish-led forces in the northeast, with the help of U.S. weapons, air power and Special Operations advisers. The United States says it will remain until there is a peace settlement, leaving open the question of how long that will be.

Turkey holds a pocket of territory in the north alongside Syrian rebels and last month launched an incursion into the adjoining Kurdish enclave of Afrin.

There, the complexity of the war is on full display. America’s NATO ally Turkey is battling U.S.-allied Kurds, who are receiving tacit support from the Syrian government. But the government is at the same time backing the tribal militias that have been attacking the U.S.-allied Kurds and their U.S. advisers in eastern Syria.

Holding the overall balance of power is Russia, which became the dominant military power in Syria when it intervened on behalf of Assad in 2015 and now is awkwardly playing the role of both combatant and peace broker.

But it is the significantly enhanced reach of Iran that poses the biggest danger of a wider conflict. Iran has provided the muscle in the form of manpower and money that enabled the Syrian government to reclaim most of the vast swaths of territory that fell out of government hands in the earliest years of the war, in the process expanding Iranian presence in Syria.

Israel has watched the expanding influence of Iran and its allied militias with growing alarm. Across its borders, Israel now faces Iranian commandos and allied forces, including the Lebanese Shiite Hezbollah movement and some of the most powerful Iraqi Shiite militias that challenged U.S. troops in Iraq a decade ago.

The weekend battle in which an Israeli warplane was shot down for the first time since the 1980s, struck by a hail of Syrian antiaircraft missiles provided by Russia, sharply raised the stakes for Israel and Iran. They now confront one another directly in Syria for the first time.

The clash in the skies was triggered by the entry of an Iranian drone into Israeli airspace. Chagai Tzuriel, director general of Israel’s Intelligence Ministry, spelled out his country’s determination to prevent Iran from maintaining its current level of influence in a postwar Syria.

“Everybody is already thinking about the day after,” he said. “The Russians and Iranians are expecting to get their fair share, having saved the regime. It just makes it more important that in this point in time we influence how Syria is shaped.”

By flying the drone into Israeli airspace, Iran had crossed a “red line,” he said.

“It was not an attack but a test of the limits and rules. For the Iranians, there is nothing better than to test the limits and get away with it, and that’s why we should not let them,” he added.

The Trump administration has been shifting its attention in Syria from the threat posed by the Islamic State to the expanded presence of Iran. Under the State Department’s Syria policy announced last month, the 2,000 troops based in northeastern ­Syria will remain, among other goals, until “Iranian influence in Syria is diminished, and Syria’s neighbors are secure from all threats emanating from Syria.”

Iran has vowed, however, that the United States will not be allowed to remain in Syria, raising the specter of overlapping U.S.-Iranian and Israeli-Iranian confrontations.

“The U.S. will not succeed in partitioning Syria,” said Ali Akbar Velayati, the foreign affairs adviser of Iran’s supreme leader, Ayatollah Ali Khamenei, according to comments published by Iran’s Mehr News Agency. “Either they will leave Eastern Euphrates in Syria or we will kick them out of there.”

He spoke last Wednesday, a day before an Iranian-backed militia made up of local tribesmen launched a large-scale attack against a military base belonging to the Kurdish-led alliance, where U.S. troops were present. The U.S. military called on helicopter gunships, fighter jets and attack aircraft to quell the assault.

The violent eruptions leave Turkey, Israel and the United States looking to Russia to de-escalate the tensions. “They are dominant in Syria and they have shown that they call the shots,” Tzuriel said. “My assumption is that Russia wants to stabilize its achievements in Syria. It has had very good achievements, now it wants to stabilize, it wants Pax Russiana.”

Many analysts question, however, whether Russia has enough influence over all the players to prevent the escalation from spiraling out of control. Russia said it was not informed by the militia that it was planning to attack the U.S.-backed base, and Russia may also not have been aware of the launch of the Iranian drone, apparently from a mobile truck, according to Israeli officials.

“The Russians have more leverage than we realize, but not as much as we would like,” said Salman Shaikh, a consultant who mediates between the Syrian factions. “This is mutating from an intra-Syrian conflict into a state-to-state conflict.”

Often forgotten in the growing rivalries are the ordinary Syrians, who continue to endure airstrikes, bombardment and, in some areas, hunger. The government has escalated its attacks on two of the biggest rebel-held ­areas since the start of the year, and the death toll is rising again. According to the Violations Documentation Center, which counts civilian casualties, 687 people died in January, and hundreds more have been killed this month.

“The Syrian war is not dying down and it won’t die down,” said Shaikh.